Functional consequences of motor unit recruitment order reversals following spinal cord transection in cat.

Motoneuron recruitment order determinations were made for acute, 2-week chronic, and 3-month chronic spinal cats by comparing cutaneous nerve stimulation thresholds for evoking single unit tibialis anterior (TA) electromyogram (EMG) spikes of different sizes. Recruitment order was largely ( approximately 80%) orderly (small spikes recruited at lower stimulus intensities than large spikes) in acute and 3-month chronic spinal animals. However, in 2-week chronic spinal animals recruitment order was reversed, with large units more often recruited at lower stimulus intensities than small units ( approximately 65%).

D-2-amino-5-phosphonovalerate, and NMDA receptor antagonist, blocks induction of associative long-term potentiation of the flexion reflex in spinal cat.

The effect of the NMDA receptor antagonist D-2-amino-5-phosphonovalerate (APV) on classical conditioning of the flexion reflex in spinal cat was examined. Animals perfused intrathecally with artificial cerebral spinal fluid (CSF) containing APV exhibited flexion reflex potentiation during the conditioning period that was not significantly different from cats receiving artificial CSF alone. However, the APV group exhibited no signs of reflex potentiation during the 2.

Retrograde labeling of lumbosacral interneurons following injections of red and green fluorescent microspheres into hindlimb motor nuclei of the cat.

In order to map the laminar and segmental positions of lumbosacral interneurons that project to L7 motor nuclei, red and green fluorescent latex microspheres ("beads") were pressure-injected through micropipettes into the deep peroneal or posterior biceps-semitendinosus motoneuron pools of cats. Micropipette tips were positioned by recording the antidromic field potentials evoked by electrical stimulation of the muscle nerves. Projecting interneurons were identified by the presence of retrogradely transported beads.

Differential synaptic effects on physiological flexor hindlimb motoneurons from cutaneous nerve inputs in spinal cat.

1. We previously demonstrated in the spinal cat that superficial peroneal cutaneous nerve stimulation produced strong reflex contraction in tibialis anterior (TA) and semitendinosus (St) muscles but unexpectedly produced mixed effects in another physiological flexor muscle, extensor digitorum longus (EDL). The goal of the present study was to further characterize the organization of ipsilateral cutaneous reflexes by examining the postsynaptic potentials (PSPs) produced in St, TA, and EDL motoneurons by superficial peroneal and saphenous nerve stimulation in decerebrate, spinal cats.

Morphological relationships among extensor digitorum longus, tibialis anterior, and semitendinosus motor nuclei of the cat: an investigation employing the retrograde transport of multiple fluorescent tracers.

To determine the morphological relationships among extensor digitorum longus (EDL), tibialis anterior (TA), and semitendinosus (St) motor nuclei in the spinal cord of the cat, these nuclei were retrogradely labeled with three different fluorescent tracers. The fluorochromes--bisbenzimide, nuclear yellow, and propidium iodide--were applied by intramuscular injection or soaking the muscle nerve. The positions of the labeled motor nuclei were bilaterally symmetrical.

Retention of a backward classically conditioned reflex response in spinal cat.

Retention of a backward classically conditioned reflex response was investigated in the spinal cat preparation. Facilitation of the flexion reflex was induced by the pairing of superficial peroneal nerve stimulation (30 Hz, 0.5 s), the US (unconditioned stimulus), with saphenous nerve stimulation (10 Hz, 1.

Evidence that the neural pathways involved in backward conditioning are different from those involved in forward conditioning.

Effects of forward and backward conditioned-unconditioned stimulus (CS-US) intervals on classical conditioning of the flexion reflex were examined in a spinal cat preparation. A less intense conditioned stimulus (CS) was employed (activation of A-alpha cutaneous fibers) compared to that of a previous study (activation of both A-alpha and A-delta cutaneous fibers). Interstimulus intervals (ISIs) ranging from +3.

Forward and backward classical conditioning of the flexion reflex in the spinal cat.

Effects of forward and backward conditioned-unconditioned stimulus (CS-US) intervals on classical conditioning of the flexion reflex were examined in a cat spinal preparation. Interstimulus intervals (ISIs) ranging from +3.0 to -3.

Retention of a classically conditioned reflex response in spinal cat.

Retention of classically conditioned flexion reflex facilitation was examined in unanesthetized, decerebrate, acute spinal cats. Flexion reflex facilitation, recorded from the tibialis anterior muscle, was obtained by pairing saphenous nerve stimulation (the conditioned stimulus) with superficial peroneal nerve stimulation (the unconditioned stimulus). The flexion reflex declined in control animals receiving the same number of nerve stimuli over the same time span, but in an explicitly unpaired sequence.

Conditioned stimulus intensity: role of cutaneous fiber size in classical conditioning of the flexion reflex in the spinal cat.

Three intensities of the conditioned stimulus (CS) were used to investigate the role of cutaneous fiber size on classical conditioning of the flexion reflex in the spinal cat. Conditioning occurred when the CS activated A alpha and A delta cutaneous fibers; CS activation of only the largest myelinated (A alpha) fibers or CS recruitment of unmyelinated (C) fibers in addition to A alpha and A delta fibers did not lead to significant conditioning. Comparison with two unpaired CS-US control treatment groups showed that the facilitation of reflex output during conditioning was specific to pairing of the CS and US and was not a consequence of sensitization or differential habituation rates between paired (conditioning) and unpaired (control) groups.

Features of laminar and somatotopic organization of lumbar spinal cord units receiving cutaneous inputs from hindlimb receptive fields.

Single-unit recordings from 312 units of lamina I-VII of the lumbar spinal cord of unanesthetized, decerebrate, T8 spinal cats were used to determine the somatotopic and laminar organization of spinal neurons responding to cutaneous stimulation of the hindlimb. Properties of cells confined to different Rexed laminae (I-VII) were shown to differ in several respects, including responses to variations in stimulus intensity, receptive-field areas, spontaneous frequencies, and central delays. Spinal cord neurons with similarly localized cutaneous receptive fields were found to be organized in sagittally oriented rectangular columns.

Classical conditioning of the flexion reflex in spinal cat: features of the reflex circuitry.

Classically conditioned facilitation of the flexor withdrawal reflex of spinal cat occurs in knee and ankle flexor muscles but not in a flexor muscle of the toes. Furthermore, the spinal circuitry activated by a component of the conditioned stimulus (A alpha cutaneous fibers) is not by itself involved in the reflex conditioning. The results suggest that increases in both cutaneous afferent output and motoneuron excitability may be eliminated as mechanisms contributing to conditioning and point to certain interneuronal pools as the locus of learning in this preparation.

Classically conditioned alterations in single motor unit activity in the spinal cat.

Muscle tension and single motor unit EMG recordings from a flexor muscle of acute spinal cats were obtained during presentation of classical conditioning and control paradigms. Conditioned increases in muscle tension were similar to previously obtained results. Motor unit recordings suggested that this conditioned reflex facilitation is brought about by an increased probability firing of motoneurons initially responsive to the conditioned stimulus, as well as orderly, size-dependent recruitment of initially non-responsive motoneurons.

Dimensions of medical students' perceptions of instruction.

Factor analysis of medical student ratings of basic science instruction yielded three dimensions of student perception of instruction: faculty-student rapport, outside work, and aspects of student comprehension. While these factors are similar to those identified in other studies, they differ in respects probably reflecting differences between medical students and other students and differences in questionnaire design.

Cardiac and respiratory conditioning, differenatiation, and extinction in the pigeon.

Paired light and foot shock in 12 pigeons rapidly developed acceleratory heart and respiratory conditioned responses. Sensitization and stimulus control birds did not condition. When a different colored stimulus light that was not reinforced was mixed in a random series with the reinforced light, rapid differentiation of both heart and respiratory responses occurred.